Neurochemical changes associated with the persistence of spontaneous oral dyskinesia in rats following chronic reserpine treatment

Effects of CATECHIN on reserpine-induced vacuous chewing movements: behavioral and biochemical analysis

This study evaluated the effect of (+)-catechin, a polyphenolic compound, on orofacial dyskinesia (OD) induced by reserpine in mice. The potential modulation of monoaminoxidase (MAO) activity, tyrosine hydroxylase (TH) and glutamic acid decarboxylase (GAD67) immunoreactivity by catechin were used as biochemical endpoints. The interaction of catechin with MAO-A and MAO-B was determined in vitro and in silico. The effects of catechin on OD induced by reserpine (1 mg/kg for 4 days, subcutaneously) in male Swiss mice were examined. After, catechin (10, 50 or 100 mg/kg, intraperitoneally) or its vehicle were given for another 20 days. On the 6th, 8th, 15th and 26th day, vacuous chewing movements (VCMs) and locomotor activity were quantified. Biochemical markers (MAO activity, TH and GAD67 immunoreactivity) were evaluated in brain structures. In vitro, catechin inhibited both MAO isoforms at concentrations of 0.34 and 1.03 mM being completely reversible for MAO-A and partially reversible for MAO-B. Molecular docking indicated that the catechin bound in the active site of MAO-A, while in the MAO-B it interacted with the surface of the enzyme in an allosteric site. In vivo, reserpine increased the VCMs and decreased the locomotor activity. Catechin (10 mg/kg), decreased the number of VCMs in the 8th day in mice pre-treated with reserpine without altering other behavioral response. Ex vivo, the MAO activity and TH and GAD67 immunoreactivity were not altered by the treatments. Catechin demonstrated a modest and transitory protective effect in a model of OD in mice.

Passiflora cincinnata Extract Delays the Development of Motor Signs and Prevents Dopaminergic Loss in a Mice Model of Parkinson's Disease

Passiflora cincinnata Masters is a Brazilian native species of passionflower. This genus is known in the American continent folk medicine for its diuretic and analgesic properties. Nevertheless, few studies investigated possible biological effects of P. cincinnata extracts. Further, evidence of antioxidant actions encourages the investigation of possible neuroprotective effects in animal models of neurodegenerative diseases. This study investigates the effect of the P. cincinnata ethanolic extract (PAS) on mice submitted to a progressive model of Parkinson's disease (PD) induced by reserpine. Male (6-month-old) mice received reserpine (0.1 mg/kg, s.c.), every other day, for 40 days, with or without a concomitant treatment with daily injections of PAS (25 mg/kg, i.p.). Catalepsy, open field, oral movements, and plus-maze discriminative avoidance evaluations were performed across treatment, and immunohistochemistry for tyrosine hydroxylase was conducted at the end. The results showed that PAS treatment delayed the onset of motor impairments and prevented the occurrence of increased catalepsy behavior in the premotor phase. However, PAS administration did not modify reserpine-induced cognitive impairments. Moreover, PAS prevented the decrease in tyrosine hydroxylase immunostaining in the substantia nigra pars compacta (SNpc) induced by reserpine. Taken together, our results suggested that PAS exerted a neuroprotective effect in a progressive model of PD.

Spontaneously Hypertensive Rats (SHR) Are Resistant to a Reserpine-Induced Progressive Model of Parkinson's Disease: Differences in Motor Behavior, Tyrosine Hydroxylase and α-Synuclein Expression

Reserpine is an irreversible inhibitor of vesicular monoamine transporter-2 (VMAT2) used to study Parkinson’s disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low-dose of reserpine was proposed as a progressive model of PD. Rats under this treatment show progressive catalepsy behavior, oral movements and spontaneous motor activity decrement. In parallel, compared to Wistar rats, spontaneously hypertensive rats (SHR) are resistant to acute reserpine-induced oral dyskinesia. We aimed to assess whether SHR would present differential susceptibility to repeated reserpine-induced deficits in the progressive model of PD. Male Wistar and SHR rats were administered 15 subcutaneously (s.c.) injections of reserpine (0.1 mg/kg) or vehicle, every other day and motor activity was assessed by the catalepsy, oral movements and open field tests. Only reserpine-treated Wistar rats presented increased latency to step down in the catalepsy test and impaired spontaneous activity in the open field. On the other hand, there was an increase in oral movements in both reserpine-treated strains, although with reduced magnitude and latency to instauration in SHR. After a 15-day withdrawn period, both strains recovered from motor impairment, but SHR animals expressed reduced latencies to reach control levels. Finally, we performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last injection or 15 days after withdrawn. Reserpine-treated animals presented a reduction in TH and an increase in α-syn immunoreactivity in the substantia nigra and dorsal striatum (dSTR), which were both recovered after 15 days of withdraw. Furthermore, SHR rats were resistant to reserpine-induced TH decrement in the substantia nigra, and presented reduced immunoreactivity to α-syn in the dSTR relative to Wistar rats, irrespective of treatment. This effect was accompanied by increase of malondaldhyde (MDA) in the striatum of reserpine-treated Wistar rats, while SHR presented reduced MDA in both control and reserpine conditions relative to Wistar strain. In conclusion, the current results show that SHR are resilient to motor and neurochemical impairments induced by the repeated low-dose reserpine protocol. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potential relevant targets to the study of susceptibility to PD.

Effect of Hypericum perforatum on different models of movement disorders in rats

The effects of Hypericum perforatum, a plant with antidepressant action, were evaluated in models of abnormal movements in rats, brought about by administration of fluphenazine or reserpine. The number of vacuous chewing movements (VCMs) and locomotor activity (the number of crossings and rears in the open field test) were measured. In experiment 1, rats received a single administration of fluphenazine enanthate (25 mg/kg, intramuscular) and/or daily treatment with H. perforatum (300 mg/kg, in place of drinking water) for 7 days. Fluphenazine increased VCMs and decreased locomotor activity. H. perforatum had no effect on either the number of VCMs or the locomotor activity. In experiment 2, rats received reserpine every 2 days for 6 days (0.5 mg/kg, subcutaneous) and/or H. perforatum (300 mg/kg, in place of drinking water) daily for 16 days beginning 10 days before the first administration of reserpine. Reserpine treatment increased VCMs and decreased locomotor activity. H. perforatum had no effect on either the number of VCMs or the number of rears but did prevent the effect of reserpine on the number of crossings. In conclusion, H. perforatum failed to protect against orofacial movements induced by fluphenazine or reserpine in rats.

Behavioral and neurochemical effects induced by reserpine in mice

RATIONALE

Reserpine, a monoamine-depleting agent, which irreversibly and non-selectively blocks the vesicular monoamine transporter, has been used as an animal model to study several neurological disorders, including tardive dyskinesia and Parkinson's disease.

OBJECTIVE

The purpose of this study was to examine if motor deficits induced by reserpine in mice could be related to alterations in the expression of dopaminergic system proteins such as tyrosine hydroxylase (TH) and dopamine transporter (DAT) and in the activity of monoamine oxidase (MAO).

METHODS

Mice received either vehicle or reserpine (0.1, 0.5, or 1 mg/kg, s.c.) for four consecutive days. Two, 20, or 60 days after reserpine withdrawal, behavioral, and neurochemical changes were evaluated.

RESULTS

Reserpine at a dose of 0.5 and 1 mg/kg increased vacuous chewing movements (VCMs) and reduced locomotion. Behavioral changes were accompanied by reduction in TH immunoreactivity in the striatum evaluated on days 2 and 20 after the last injection of 1 mg/kg reserpine. Furthermore, negative correlations were found between VCM and MAO-A or MAO-B on day 2 and TH striatal immunoreactivity on day 20 after the last injection of 1 mg/kg reserpine. A positive correlation was observed between VCMs and DAT immunoreactivity in the substantia nigra on day 2 after the last injection of 0.5 mg/kg reserpine.

CONCLUSIONS

These findings suggest that the pharmacological blockage of vesicular monoamine transporter (VMAT) by reserpine caused neurochemical and behavioral alterations in mice.

Molecular, Neurochemical, and Behavioral Hallmarks of Reserpine as a Model for Parkinson's Disease: New Perspectives to a Long-Standing Model

The administration of reserpine to rodents was one of the first models used to investigate the pathophysiology and screening for potential treatments of Parkinson's disease (PD). The reserpine model was critical to the understanding of the role of monoamine system in the regulation of motor and affective disorders, as well as the efficacy of current PD treatments, such as L-DOPA and dopamine agonists. Nevertheless, with the introduction of toxin-induced and genetic models of PD, reserpine became underused. The main rationale to this drawback was the supposed absence of reserpine construct validity with PD. Here, we highlight classical and recent experimental findings that support the face, pharmacological, and construct validity of reserpine PD model and reason against the current rationale for its underuse. We also aim to shed a new perspective upon the model by discussing the main challenges and potentials for the reserpine model of PD.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

Effect of Withania somnifera root extract on reserpine-induced orofacial dyskinesia and cognitive dysfunction

Tardive dyskinesia is one of the major side effects of long-term neuroleptic treatment. The pathophysiology of this disabling and commonly irreversible movement disorder is still obscure. Vacuous chewing movements in rats are widely accepted as an animal model of tardive dyskinesia. Oxidative stress and products of lipid peroxidation are implicated in the pathophysiology of tardive dyskinesia. Repeated treatment with reserpine (1.0 mg/kg) on alternate days for a period of 5 days (days 1, 3 and 5) significantly induced vacuous chewing movements and tongue protrusions in rats. Chronic treatment with Withania somnifera root extract (Ws) for a period of 4 weeks to reserpine treated animals significantly and dose dependently (50 and 100 mg/kg) reduced the reserpine-induced vacuous chewing movements and tongue protrusions. Reserpine treated animals also showed poor retention of memory in the elevated plus maze task paradigm. Chronic Ws administration significantly reversed reserpine-induced retention deficits. Biochemical analysis revealed that chronic reserpine treatment significantly induced lipid peroxidation and decreased the glutathione (GSH) levels in the brains of rats. Chronic reserpine treated rats showed decreased levels of antioxidant defense enzymes, superoxide dismutase (SOD) and catalase. Chronic administration of Ws root extract dose dependently (50 and 100 mg/kg) and significantly reduced the lipid peroxidation and restored the decreased glutathione levels by chronic reserpine treatment. It also significantly reversed the reserpine-induced decrease in brain SOD and catalase levels in rats. The major findings of the present study indicate that oxidative stress might play an important role in the pathophysiology of reserpine-induced abnormal oral movements. In conclusion, Withania somnifera root extract could be a useful drug for the treatment of drug-induced dyskinesia.

Effects of baclofen on reserpine-induced vacuous chewing movements in mice

We have described that GABA mimetic drugs present the ability to inhibit the expression of reserpine-induced oral movements. In this respect, oral movements is associated with important neuropathologies. This study investigates the effects of an acute or a repeated treatment of different doses of the GABA(B) agonist baclofen, as well as withdrawal from these treatments, on the development and/or expression of reserpine-induced vacuous chewing movements (VCM). Male mice received two injections of vehicle or of 1mg/kg reserpine separated by 48 h. In the first experiment, 24h later, animals were acutely treated with vehicle or baclofen (1, 2 or 4 mg/kg). In the second experiment, animals were treated with vehicle or baclofen (1 or 4 mg/kg) for four consecutive days receiving a concomitant injection of 1mg/kg reserpine (or vehicle) on Days 2 and 4. Twenty-four hours later, animals received vehicle or baclofen. Thirty minutes after the last injection, they were observed for quantification of VCM and open-field general activity. The acute administration of all the doses of baclofen abolished the manifestation of reserpine-induced VCM. Repeated treatment with 1mg/kg baclofen induced tolerance to the ability of an acute injection of this dose to reduce VCM. Treatment with baclofen (4 mg/kg) did not modify spontaneous VCM. Acute administration of the highest dose induced a decrease in general motor activity and a potentiation of the reserpine-induced decrease in general activity. These results reinforce the involvement of GABAergic hypofunction in the expression of oral movements and suggest that a repeated treatment with baclofen induces compensatory changes in GABAergic transmission that can attenuate its acute property to decrease VCM.

Effects of gabaergic drugs on reserpine-induced oral dyskinesia

Recently we have described the antidyskinetic property of the GABA mimetic drugs valproic acid and topiramate on reserpine-induced oral dyskinesia. In this respect, oral dyskinesia has been associated with important neuropathologies. The present study investigates the effects of different doses of the GABA(A) agonist tetrahydroisoxazolopyridine (THIP), of the GABA(B) agonist baclofen as well as of the GABA(A) modulator diazepam on the manifestation of reserpine-induced orofacial dyskinesia. Male Wistar rats received two injections of vehicle or of 1mg/kg reserpine separated by 48 h. Twenty-four hours later, animals were acutely treated with vehicle or THIP (2, 4 or 8 mg/kg), baclofen (1, 2 or 4 mg/kg) or diazepam (1, 2 or 4 mg/kg) and were observed for quantification of oral dyskinesia and open-field general activity. In order to verify the effects of these drugs per se on spontaneous oral movements, male Wistar rats were acutely treated with vehicle, 8 mg/kg THIP, 4 mg/kg baclofen or 4 mg/kg diazepam and observed for quantification of oral dyskinesia. The two highest doses of THIP or of baclofen abolished the manifestation of reserpine-induced oral dyskinesia while the lowest dose of baclofen attenuated it. Diazepam did not modify reserpine-induced oral dyskinesia at any dose tested. The highest doses of these drugs did not modify spontaneous oral movements. Reserpine-induced decrease in open-field general activity was not modified by any of the doses of THIP and diazepam or by the two lowest doses of baclofen. The highest dose of baclofen potentiated the increase in the duration of immobility induced by reserpine. These results reinforce the involvement of GABAergic hypofunction in the expression of oral dyskinesias, and support the potential therapeutic use of THIP and baclofen in the treatment of oral dyskinesias.

Acute reserpine and subchronic haloperidol treatments change synaptosomal brain glutamate uptake and elicit orofacial dyskinesia in rats

Reserpine- and haloperidol-induced orofacial dyskinesia are putative animal models of tardive dyskinesia (TD) whose pathophysiology has been related to free radical generation and oxidative stress. In the present study, the authors induced orofacial dyskinesia by acute reserpine and subchronic haloperidol administration to rats. Reserpine injection (one dose of 1 mg/kg s.c.) every other day for 3 days caused a significant increase in vacuous chewing, tongue protrusion and duration of facial twitching, compared to the control. Haloperidol administration (one dose of 12 mg/kg once a week s.c.) for 4 weeks caused an increase in vacuous chewing, tongue protrusion and duration of facial twitching observed in four weekly evaluations. After the treatments and behavioral observation, glutamate uptake by segments of the brain was analyzed. A decreased glutamate uptake was observed in the subcortical parts of animals treated with reserpine and haloperidol, compared to the control. Importantly, a decrease in glutamate uptake correlates negatively with an increase in the incidence of orofacial diskinesia. These results indicate that early changes in glutamate transport may be related to the development of vacuous chewing movements in rats.

Effects of topiramate on oral dyskinesia induced by reserpine

Recently, we have described the antidyskinetic property of the GABA mimetic drug valproic acid on reserpine-induced oral dyskinesia, an animal model that has been related to tardive as well as acute dyskinesias, which are associated with important neuropathologies. The present study investigates the effects of different doses of the GABA mimetic anticonvulsant topiramate on the manifestation of reserpine-induced orofacial dyskinesia. Female EPM-M1 mice received two injections of control solution or of 0.5 mg/kg reserpine separated by 48 h. Twenty-four hours after the second reserpine or control solution injection, animals were acutely treated with control solution or topiramate (1, 3, 10 or 30 mg/kg) and were observed for quantification of oral dyskinesia or general activity in an open-field. In order to verify the effects of topiramate per se on oral dyskinesia or general activity, female EPM-M1 mice were acutely treated with control solution or 1, 3, 10 or 30 mg/kg topiramate and observed for quantification of oral dyskinesia and general activity. The highest dose of topiramate completely abolished the manifestation of reserpine-induced oral dyskinesia whereas the doses of 3 and 10 mg/kg significantly attenuated it. None of the doses of the anticonvulsant modified spontaneous locomotion frequency or oral movements, whereas spontaneous rearing frequency was decreased by 3, 10 and 30 mg/kg topiramate. The highest dose of topiramate did not modify general activity in reserpine-treated mice. These results support the potential therapeutic use of topiramate in the treatment of oral dyskinesias.

Reversal of Reserpine-Induced Orofacial Dyskinesia and Cognitive Dysfunction by Quercetin

Tardive dyskinesia (TD) is a serious neurological syndrome associated with long-term administration of neuroleptics to humans and experimental animals. The pathophysiology of this disabling and commonly irreversible movement disorder is still obscure. It may be caused by a loss of dopaminergic cells or may be due to free radicals as a product of high synaptic dopamine levels. Quercetin is a bioflavonoid with strong antioxidant properties. Repeated treatment with reserpine (1.0 mg/kg) on each other day for a period of 5 days (days 1, 3 and 5) significantly induced vacuous chewing movements (VCMs) and tongue protrusions (TPs) in rats. Chronic treatment with quercetin for a period of 4 weeks to reserpine-treated animals significantly and dose dependently (50 and 100 mg/kg) reduced the reserpine-induced VCMs and TPs. Reserpine-treated animals also showed poor retention of memory in elevated plus-maze task paradigm. Chronic quercetin administration significantly reversed reserpine-induced retention deficits. Biochemical analysis revealed that chronic reserpine treatment significantly induced lipid peroxidation and decreased the glutathione (GSH) levels in the brains of rats. Chronic reserpine-treated rats showed decreased levels of antioxidant defense enzymes, superoxide dismutase (SOD) and catalase. Chronic administration of quercetin dose dependently (50-100 mg/kg) and significantly reduced the lipid peroxidation and restored the decreased GSH levels by chronic reserpine treatment. It also significantly reversed the reserpine-induced decrease in brain SOD and catalase levels in rats. The results of the present study clearly indicated that quercetin has a protective role against reserpine-induced orofacial dyskinesia and memory impairment. Consequently, the use of quercetin as a therapeutic agent for the treatment of TD should be considered.

Dopamine depletion and in vivo binding of PET D1 receptor radioligands: implications for imaging studies in schizophrenia

Recent positron emission tomography (PET) studies have assessed the level of dopamine (DA) D1 receptors in the prefrontal cortex (PFC) in patients with schizophrenia and have generated contradictory findings. In the PFC of patients with schizophrenia, the binding potential (BP) of [11C]NNC 112 has been reported as increased, while the BP of [11C]SCH 23390 was reported as decreased or unchanged. In this study, the effect of acute and subchronic DA depletion on the in vivo binding of [11C]NNC 112 and [3H]SCH 23390 was evaluated in rats. Acute DA depletion did not affect [11C]NNC 112 in vivo binding, but paradoxically decreased [3H]SCH 23390 in vivo binding. Subchronic DA depletion was associated with increased [11C]NNC 112 in vivo binding and decreased [3H]SCH 23390 in vivo binding. Together, these data demonstrate that the in vivo binding of these radiotracers is differentially affected by changes in endogenous DA tone, and suggest that alterations in the binding of these tracers in the PFC of patients with schizophrenia might reflect changes in D1 receptors secondary to sustained deficit in prefrontal DA function.

Effects of valproic acid on an animal model of tardive dyskinesia

GABAergic hypofunction in the basal ganglia is stated as an important mechanism underlying the pathophysiology of tardive dyskinesia. The present study investigates the effects of the GABA-mimetic drug valproic acid (VA) on the manifestation of reserpine-induced orofacial movements, an animal model of tardive dyskinesia. Male Wistar rats received two injections of control solution or of 1 mg/kg reserpine separated by 48 h. Twenty-four hours later, animals were acutely treated with 50, 100, or 200 mg/kg VA or control solution and were observed for quantification of orofacial movements and of open-field general activity. The highest dose of VA inhibited the manifestation of reserpine-induced orofacial movements but none of the VA doses modified reserpine-induced decrease in open-field general activity. These results support the potential of VA as an effective pharmacological tool in the treatment of tardive dyskinesia.

Antidyskinetic effects of risperidone on animal models of tardive dyskinesia in mice

The effects of risperidone, an atypical neuroleptic, were investigated on two animal models of tardive dyskinesia (TD). The repeated administration of reserpine (1.0mg/kg) or haloperidol (2.0mg/kg) induces orofacial movements in mice, which are very similar to those observed in humans presenting TD. The effects of acute or repeated treatment with several doses of risperidone (0.1; 0.5; 2.0 or 4.0) on the expression and development of orofacial movements in reserpine- and haloperidol-treated male mice were investigated. The results showed that risperidone per se did not induce the development of orofacial movements. In addition, this drug was able to attenuate the expression and the development of reserpine-as well as haloperidol-induced orofacial movements. These results are in line with several clinical studies that suggest not only a lower incidence of TD in schizophrenic patients treated with risperidone, but also an antidyskinetic effect of this drug in patients previously treated with classical neuroleptics.

Ebselen attenuates reserpine-induced orofacial dyskinesia and oxidative stress in rat striatum

Reserpine-induced orofacial dyskinesia is an alleged animal model of tardive dyskinesia whose pathophysiology has been related to striatal oxidative stress. In the present investigation, the authors examined whether ebselen, an antioxidant organochalcogen with glutathione peroxidase-like activity, changes the behavioral and neurochemical effect of acute reserpine administration. Reserpine injection for 3 days every other day caused a significant increase on the tongue protrusion frequency and ebselen (30 mg/kg ip for 4 days, starting 1 day before reserpine) reversed partially the effect of reserpine (P<.05). Reserpine- and reserpine+ebselen-treated groups displayed an increase in vacuous chewing frequency when compared to control and ebselen-treated groups (P<.05) Reserpine increased the duration of facial twitching and ebselen reversed partially the effect of reserpine (P<.01). Reserpine increased significantly the thiobarbituric acid-reactive species (TBARS) levels, and ebselen reversed the effect of reserpine on TBARS production in rat striatum. The results of the present study clearly indicated that ebselen has a protective role against reserpine-induced orofacial dyskinesia and reversed the increase in TBARS production caused by reserpine administration. Consequently, the use of ebselen as a therapeutic agent for the treatment of tardive dyskinesia should be considered.

Concomitant development of oral dyskinesia and memory deficits in reserpine-treated male and female mice

It has been suggested that reserpine-induced oral dyskinesia in rats may provide a new animal model of tardive dyskinesia. Both cognitive deficits and gender have been associated with the development of tardive dyskinesia. The aim of the present study was to investigate the effects of reserpine administration on the development of orofacial dyskinesia and on plus-maze discriminative avoidance task (DAT-an animal model of associative learning) in male and female mice. Male and female mice received 1.0 mg/kg reserpine or saline subcutaneously on day 1. On days 3, 6 and 8, the frequency of vacuous chewing movements (VCM) was quantified. On day 6, the DAT conditioning was performed, in a modified elevated plus-maze. In one of the enclosed arms, the animals received aversive stimulation (light and noise). On day 8, a test session was performed and the time spent by the animals in each of the enclosed arms was recorded. Our results showed that reserpine-treated male and female mice presented significantly higher VCM when compared with respective control groups in all observation days. On day 6, reserpine-treated female mice presented significantly higher VCM when compared with male mice injected with this drug. The DAT test performed on day 8 showed that the time spent in the aversive arm by saline-treated mice was significantly lower than the time spent in the non-aversive arm. This difference was not observed for reserpine-treated mice. Our results demonstrate the development of reserpine-induced oral dyskinesia in both male and female mice. While this oral dyskinesia is accompanied by a cognitive deficit in both genders, female mice tended to have more severe oral dyskinesia. It is suggested that reserpine-induced oral dyskinesia may provide a quick, simple and efficient mouse model of tardive dyskinesia.

Behavioral effects of MK-801 on reserpine-treated mice

The effects of dizocilpine (MK-801), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, were studied on dopamine-related behaviors induced by reserpine treatments. This study focuses on behavioral syndromes that may used as models for Parkinson's disease, or tardive dyskinesia, and its response after glutamatergic blockage. Reserpine (1 mg/kg), administered once every other day for 4 days, produced increases in orofacial dyskinesia, tongue protrusion and vacuous chewing in mice, which are signs indicative of tardive dyskinesia. Reserpine also produced tremor and catalepsy, which are signs suggestive of Parkinson's disease. MK-801 (0.1 mg/kg), administered 30 min before the observation test, prevented the vacuous chewing movements, tongue protrusions and catalepsy induced by reserpine. However, MK-801 injection produced a significant increase of tremor in reserpine-treated mice. Reserpine (1 mg/kg), administered 90 min before the test and followed by apomophine injection (0.1 mg/kg) 5 min before the test, did not produce oral dyskinesia in mice. On the other hand, reserpine induced increases in tremor and catalepsy compared to control mice. MK-801 (0.1 mg/kg) administration attenuated the catalepsy and tremor induced by reserpine. Pretreatment with reserpine (1 mg/kg) 24 h before the observation test produced increases in vacuous chewing movements and tongue protrusion, as well as increases in tremor and catalepsy, whereas MK-801 (0.1 mg/kg) injection 90 min before the test reversed the effects of reserpine. These results show that reserpine produces different and abnormal movements, which are related to dose and schedule employed and can be considered as parkinsonian-like and tardive dsykinesia signs. The glutamatergic blockage produced by NMDA can restore these signs, such as vacuous chewing movements, tongue protrusions, catalepsy and tremor according to the employed model.

The mitochondrial toxin 3-nitropropionic acid aggravates reserpine-induced oral dyskinesia in rats

The effects of a previous long-term administration of the mitochondrial toxin 3-nitropropionic acid were studied on an animal model of tardive dyskinesia, i.e., the frequency of spontaneous tongue protrusions in rats repeatedly treated with reserpine. 3-Nitropropionic acid (10 or 15 mg/kg i.p., every other day for 17 days) potentiated the increase in tongue-protrusion frequency induced by reserpine (1 mg/kg, s.c., every other day for 3 days) but did not modify reserpine-induced increase in immobility duration and decrease in locomotion frequency. These results support the notion that neurotoxic events are associated with the development of tardive dyskinesia.

Effects of buspirone on an animal model of tardive dyskinesia

1. The effects of buspirone were studied on an animal model of tardive dyskinesia, i.e., the quantification of orofacial dyskinesia in rats repeatedly treated with reserpine. 2. Rats were co-treated with saline [SAL] or buspirone [BUS] (3.0 mg/kg, i.p., twice daily) and vehicle [VEH] or reserpine [RES] (0.1 mg/kg, s.c., once every other day) for 19 days. On the day 20, the animals were observed for quantification of the behavioral parameters of orofacial dyskinesia: tongue protrusion and vacuous chewing movements frequencies and duration of twitching of the facial musculature. 3. Rats of the SAL + RES group exhibited a significant increase in the three behavioral parameters of orofacial dyskinesia relative to the rats of the SAL + VEH group. However, animals of the BUS + RES group showed only an increased frequency of vacuous chewing movements when compared to animals of the SAL + VEH group. In addition, the duration of the facial twitching was significantly decreased in the BUS + RES group in relation to rats of the SAL + RES group. There were no significant differences in the orofacial parameters between the BUS + VEH and the SAL + VEH groups. 4. Because it was also verified that chronic buspirone treatment was able to increase apomorphine-induced yawning behavior, the possibility is raised that buspirone attenuates reserpine-induced orofacial dyskinesia through the development of dopamine autoreceptor supersensitivity.

Reserpine does not induce orofacial dyskinesia in spontaneously hypertensive rats

The nigrostriatal dopaminergic system seems to be involved in both reserpine-induced orofacial dyskinesia in normal rats and in the pathogenesis of hypertension in spontaneously hypertensive rats. In the present study, repeated reserpine administration (1.0 mg/kg, s.c., every other day, for 3 days) increased tongue protrusion and vacuous chewing frequencies as well as the duration of facial twitching in Wistar normotensive but not in spontaneously hypertensive rats. These results suggest that genetic hypertension and drug-induced orofacial movements may be inversely modulated by similar mechanisms in the nigrostriatal dopaminergic system.

Effects of age on a new animal model of tardive dyskinesia

The effects of age were studied on a new animal model of tardive dyskinesia, i.e., the quantification of oral dyskinesia in rats repeatedly treated with reserpine. Adult and old rats received two injections of reserpine (0.5 or 1.0 mg/kg s.c.) or vehicle, separated by 48 h. One, 10, 25 and 40 days after the second injection of reserpine or vehicle, the animals were observed for quantification of the behavioral parameters of oral dyskinesia: tongue protrusion and vacuous chewing movement frequencies and duration of twitching of the facial musculature. Phenomenologically, control old rats and reserpine-treated adult animals showed very similar oral dyskinesia. When compared to control adult rats, the significant increase in tongue protrusion frequency induced by reserpine treatment was more persistent in the old rats than in the adult animals. Because it is well known that age increases the persistence of tardive dyskinesia, our data provide further support for the validation of reserpine-induced oral dyskinesia as an animal model of tardive dyskinesia. In addition, the possibility is raised that a common pathophysiological mechanism may underlie tardive dyskinesia and age- and reserpine-induced oral dyskinesia.

Acute reserpine administration elicits long-term spontaneous oral dyskinesia

Chronic reserpine administration produces persistent oral dyskinesia accompanied by severe dopamine depletion in the caudate-putamen. The present study examined whether these behavioral and neurochemical effects would persist following acute reserpine administration. Acute administration of reserpine (1 mg/kg, s.c.) produced spontaneous oral dyskinesia that persisted above control levels for at least 84 days. Reserpine also produced a 74% depletion of dopamine in the caudate-putamen relative to vehicle treatment at 3 days post-injection, but did not significantly alter dopamine in the caudate-putamen at 84 days post-injection. The finding that reserpine-induced oral dyskinesia persisted despite repletion of dopamine in the caudate-putamen suggests that the persistent neuropathological change underlying this behavior occurs in a neural pathway other than the dopaminergic nigrostriatal pathway.

Effects of monosialoganglioside on a new model of tardive dyskinesia

1- The effects of monosialoganglioside GM1 were studied on a new model of tardive dyskinesia, i.e., the frequency of spontaneous tongue protrusions in rats repeatedly treated with reserpine. 2- Rats were co-treated with vehicle (VEH) or reserpine (RES) (0.1 mg/kg, s.c., every other day) and saline (SAL) or GM1 (5 mg/kg, i.p., every day) for 30 days and observed for tongue protrusions on days 10, 20 and 30. 3- During each test day animals of the RES + SAL group exhibited an increase in tongue protrusions relative to rats of the VEH + SAL group. However, rats of the RES + GM1 group showed an increased frequency of tongue protrusions only on day 10, when compared to animals of the VEH + SAL group. There were no significant differences in tongue protrusion frequency between the VEH + GM1 and the VEH + SAL groups. 4- These results differ from previous studies which reported a facilitatory effect of GM1 co-administration on conventional behavioral animal models of tardive dyskinesia. The possibility is raised that GM1 attenuates the reserpine-induced increase in tongue protrusions through its protective effect on glutamate/oxidative stress neurotoxicity.

Effects of amphetamine and 6-hydroxydopamine lesions on reserpine-induced oral dyskinesia

The present study examined whether reserpine-induced oral dyskinesia is mediated by release of residual endogenous dopamine. Amphetamine produced a dose-dependent change in reserpine-induced oral dyskinesia in which the response was exacerbated by 0.6 mg/kg amphetamine and inhibited by 1 mg/kg. The latter dose also produced stereotypy that may have interfered with expression of reserpine-induced oral dyskinesia. Nigrostriatal 6-hydroxydopamine lesions attenuated expression of reserpine-induced oral dyskinesia. These lesions did not reduce locomotor activity, however, indicating that the attenuation of reserpine-induced oral dyskinesia was not due to a general depressant effect of the lesions on motor behavior. These results suggest that increasing dopamine release by administration of amphetamine exacerbates reserpine-induced oral dyskinesia, whereas decreasing the amount of releasable dopamine in the striatum by 6-hydroxydopamine lesions attenuates reserpine-induced oral dyskinsia. These findings may have implications for understanding tardive dyskinesia and L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia.

Suppression of oro-facial movements by rolipram, a cAMP phosphodiesterase inhibitor, in rats chronically treated with haloperidol

We investigated the effects of rolipram, a selective cyclic adenosine 3',5'-monophosphate phosphodiesterase type IV inhibitor, and isobutylmethylxanthine, a nonselective phosphodiesterase inhibitor, on purposeless spontaneous chewing movements and tongue protrusions produced by 24 weeks treatment with haloperidol decanoate (25 mg/kg every 4 weeks i.m.) in rats, to examine our hypothesis that restoration of striatal cyclic adenosine 3',5'-monophosphate levels previously reduced due to dopamine D2 receptor supersensitivity, may suppress these movements. Tests were performed 8 weeks after the final injection. Haloperidol treatment significantly increased dyskinetic movements and striatal dopamine D2 receptor density compared with controls. Rolipram (0.1-1.0 mg/kg i.p.) suppressed these movements in a dose-dependent manner, whereas isobutylmethylxanthine (2 mg/kg i.p.) only slightly suppressed the syndrome and doses higher than 5 mg/kg i.p. produced other intensive movements. These results support our hypothesis and suggest that rolipram may have a therapeutic effect on tardive dyskinesia.

Rolipram, a selective c-AMP phosphodiesterase inhibitor suppresses oro-facial dyskinetic movements in rats

Since striatal dopamine D2 receptor supersensitivity in the etiology of tardive dyskinesia has been suggested and dopamine D2 receptors are known to inhibit adenylate cyclase activity resulting in a decrease of cyclic adenosine 3',5'-monophosphate (cAMP) levels, we hypothesized that an increase in cAMP levels ameliorates the condition. In the present study, 21-day haloperidol treatment (1.5 mg/kg I.P.) in rats resulted in an increase in striatal [3H]-spiperone (D2) binding whereas [3H] SCH23390 (D1) binding was unaltered. This haloperidol treatment also induced a significantly increase in the frequency of involuntary chewing movements and tongue protrusions, which are considered as a model of tardive dyskinesia. These dyskinetic movements were suppressed by administration of rolipram (0.5 and 1.0 mg/kg I.P.), an inhibitor of the cAMP phosphodiesterase type IV. The present results suggest that selective cAMP phosphodiesterase type IV inhibitors could be putative therapeutic drugs for tardive dyskinesia.

Dose-dependent differences in the development of reserpine-induced oral dyskinesia in rats: support for a model of tardive dyskinesia

Rats treated with reserpine develop spontaneous orofacial dyskinesia that has features similar to tardive dyskinesia (TD) in humans. In contrast to TD, however, reserpine-induced oral dyskinesia develops rapidly reaching a maximal level within 3 days at a dose of 1 mg/kg per day. The present study examined whether rats administered lower doses of reserpine would develop the oral dyskinesia at a slower rate, similar to the protracted development of TD. Rats were administered 0, 0.01, 0.05, 0.1, or 1.0 mg/kg reserpine subcutaneously every other day for 100 days. Oral dyskinesia was measured by recording the incidence of tongue protrusions for 30 min on days 1, 4, 10, 20, 40, 60, and 100. The time course of the development of reserpine-induced oral dyskinesia varied dose-dependently. The response was evident within 4 days at 1 mg/kg, within 20 days at 0.1 mg/kg, within 60 days at 0.05 mg/kg, and was not evident at 0.01 mg/kg at any time during the 100 days of treatment. The protracted development of reserpine-induced oral dyskinesia at the lower doses is consistent with TD. Doses of reserpine that produced an increase in tongue protrusions also produced a 90-95% depletion of dopamine and an increase in the ratio of dopamine metabolites to dopamine in the caudate-putamen. The disruption of dopamine neurotransmission may be involved in development of the oral dyskinesia. Furthermore, it is suggested that the 1 mg/kg dose of reserpine may induce neurochemical changes similar to that produced by long-term neuroleptic treatment, but at an accelerated rate, thereby providing a new efficient model of TD.

Vacuous jaw movements in rats induced by acute reserpine administration: interactions with different doses of apomorphine

Two experiments were conducted to study the vacuous jaw movements induced in rats by acute administration of the monoamine-depleting agent reserpine. In the first experiment, different doses of reserpine (1.25, 2.5, and 5.0 mg/kg) were assessed for their ability to induce vacuous jaw movements. Acute administration of reserpine induced a dose-related increase in vacuous jaw movements, with the two highest doses being significantly different from the vehicle control. In the second experiment, interactions between 5.0 mg/kg reserpine and the dopamine agonist apomorphine were investigated. Coadministration of reserpine with the lowest dose of apomorphine (0.1 mg/kg) significantly increased vacuous jaw movements relative to reserpine alone. The two higher doses of apomorphine (0.5 and 1.0 mg/kg) significantly decreased vacuous jaw movements in reserpine-treated rats. These results demonstrate that vacuous jaw movements are induced by acute reserpine treatment in a dose-related manner. In addition, the interactions with apomorphine suggest that vacuous jaw movements are stimulated by decreases in dopamine release produced by low doses of apomorphine that are thought to have mainly presynaptic actions, but that these movements are decreased by higher doses of apomorphine that are known to act postsynaptically.

Effects of acute haloperidol and reserpine administration on vacuous jaw movements in three different age groups of rats

In these experiments three different age groups of rats were tested for vacuous jaw movements. The age groups included rats aged 3 months, rats aged 6-9 months, and rats aged 12-15 months. In the first experiment, rats were given a single IP injection of either 0.3% tartaric acid vehicle or 0.4 mg/kg haloperidol. In the second experiment, rats were given injections of vehicle or 5.0 mg/kg reserpine. Haloperidol and reserpine significantly increased vacuous jaw movements. There were significant effects of age on vacuous jaw movements, with rats aged 6-9 months and rats aged 12-15 months showing more jaw movements than 3-month-old rats. In both experiments, the drug x age interaction was not significant, indicating that the combined effects of age and neuroleptic treatment were additive and not synergistic. Haloperidol and reserpine also reduced rearing behavior in all age groups. It is concluded that age is an important variable in studies of vacuous jaw movements.